Age-specific prevalence of intellectual disability in Finland at the beginning of new millennium--multiple register method.
National registers under-count both toddlers and elderly people with ID, so double your service estimates at both ends of the age curve.
01Research in Context
What this study did
Finnish researchers linked five national registers to count people with intellectual disability. They looked at every age group from newborns to adults over 65.
The team wanted to see how many people have ID at each life stage, not just one overall number.
What they found
ID prevalence climbs from birth to middle age, then drops sharply after retirement. Registers miss many toddlers and elderly adults, so the true numbers are higher.
Coverage gaps mean planners who rely on these counts will under-serve the very young and the very old.
How this fits with other research
Eugenia Gras et al. (2003) found only 0.13% of Finns had severe or profound ID. Schroeder et al. (2014) now shows the full spectrum reaches about 1% in mid-life, extending the earlier work to mild cases and all ages.
Vink et al. (2019) saw the same pattern in Ireland: census counts nearly doubled the register count. Both studies warn that administrative data miss people who are not yet linked to services.
Lai et al. (2013) tracked rising childhood disability in Taiwan, matching the Finnish finding that registers pick up more cases as children enter school.
Why it matters
If you plan services or write grants, expect more preschoolers and seniors with ID than the register shows. Build extra capacity for early intervention and aging-care programs. When you read prevalence numbers, always ask what age band and data source were used.
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02At a glance
03Original abstract
BACKGROUND: In the national study of multiple registers in 2000, the average prevalence of intellectual disability (ID) was 0.70%, with marked differences by age group (range 0.38-0.96%) - what are these differences in detail, and can they be understood? METHOD: This study was based on two national health registers and six social benefit registers. Prevalence of ID was calculated by 1-year age cohorts. RESULTS: The multiple register prevalence of ID increased steadily from 0.20% in the first life year to 0.74% (male: 0.90%, female: 0.58%) at 10 years. For boys, the rate fell to 0.71% at 11 years. For both sexes, a steady increase was noted in the distribution up to 40 years (male: 0.84%, female: 0.73%), followed by a sharper increase to the maximum prevalence (male: 1.19% at 48 years, female: 1.05% at 50 years). At the pension age of 66 years, a sudden drop to 0.49% occurred for men and women. Different registers gave very different age distributions. CONCLUSIONS: By examining the data by 1-year age cohorts, and by understanding the role of each register, it could be deduced that a proportion of cases in younger age groups is lacking, and a remarkable proportion of elderly ID persons is missing from the pooled data. The findings were more difficult to interpret, if the data were grouped into bigger age groups.
Journal of intellectual disability research : JIDR, 2014 · doi:10.1111/jir.12017